This invention relates generally to a nuclear research reactor, and more particularly to an ultra high thermal neutron flux reactor.
High flux research reactors are presently used for a variety of research and testing purposes, including neutron beam research, isotope production, and materials testing. The current state of the art reactors produce flux levels of about 10.sup.15 n/cm.sup.2 s. Production of these flux levels requires generation of core power densities of 2-3 MW/L. Table 1 lists the performance characteristics of current generation, high flux research and test reactors. These reactors include the High Flux Reactor at Institut Lane Langein (ILL) (Grenoble), the High Flux Beam Reactor at Brookhaven National Laboratory (BNL), the High Flux Isotope Reactor at Oak Ridge National Laboratory (ORNL) and the Advanced Test Reactor at Idaho National Engineering Laboratory (INEL).
TABLE I ______________________________________ Operating Characteristics of Research Reactors HFR HFBR HFIR ATR (ILL) (BNL) (ORNL) (INEL) ______________________________________ Power (MW) 57 60 100 250 Coolant D.sub.2 O D.sub.2 O H.sub.2 O H.sub.2 O Reflector D.sub.2 O D.sub.2 O Be Be Core volume (L) 46 100 50.9 275 Average power density 1.14 0.60 1.96 0.92 (MW/L) Peak power density -- 2.1 3.1 3.5 (MW/L) Peak surface heat flux 5.0 4.2 3.9 7.0 (MW/m.sup.2) Peak unperturbed thermal 1.5 1.05 1.3 0.85 flux (10.sup.15 n/(cm.sup.2 s) ______________________________________
There is currently an identified need within the research community for an advanced steady-state neutron source with a flux level ten times that of the existing sources. The key to meeting this identified need is the production of a thermal neutron flux of at least 10.sup.16 n/cm.sup.2 s in an ex-core environment which is suitable for a large number of research instruments including hot neutron sources (high temperature graphite) and cold neutron sources (cryogenic sources to scatter neutrons to low energies), neutron beam and guide tubes, materials and irradiation testing, and isotope research. Production of high values of neutron flux requires high fission rate densities (and therefore, high power densities). To obtain an order of magnitude increase in neutron flux, approximately an order of magnitude is required in fission source (power) density compared with current generation high flux research reactors. Small incremental performance gains can be made by flattening the core power distribution with a combination of heavy water coolant and finer gradations in fuel loading, increasing the coolant flow and pressure, and making the core more compact, but these alone will not permit the core power density to be increased sufficiently to produce the desired 10.sup.16 n/cm.sup.2 s flux. Small, compact core volumes are highly desirable to keep the total reactor power as low as possible. The required high core power density results in relatively high heat flux values which present a major challenge to cooling the core. Operation at ultra-high core power densities produces high hot-stripe coolant and fuel plate temperatures, which may exceed critical heat flux and flow instability safety limits. These conditions are a function of coolant mass flow rate, coolant and plate temperatures, surface heat flux conditions, coolant channel geometry and characteristics, and coolant pressure. Critical heat flux is a local cooling disruption that usually occurs at the point of highest heat flux. Flow instability is the process in which boiling in a thin channel produces a transient flow condition that can proceed to fuel plate burnout. Flow instability is linked to the coolant temperatures produced by a hot-stripe along the length of a coolant channel to which poorly mixed coolant flow is exposed. Further, high temperature core conditions lead to the buildup of a thermal-insulating aluminum oxide layer on the fuel plate, which ultimately could lead to the fuel exceeding its melting limits. Therefore in view of these limitations, attainment of the 10.sup.16 n/cm.sup.2 s flux goal cannot be accomplished by a straightforward extrapulation of current technology.
An additional disadvantage to conventional high flux research reactors is that the neutron beam tubes must be orientated tangentially to the core. This tangential orientation is required to prevent exposing the field-of-view of the beam tubes to fast neutrons and gammas produced in the core. It is desirable to have direct radial beam access to the high flux environment. Direct radial beam orientation allows more beams to be packed around the core, and exposes less structural tube material to the high flux environment than tangential orientation. A partial split core arrangement is utilized in the National Bureau of Standards Reactor to help reduce fast neutron and gamma background in the beams.
Therefore, in view of the above, it is an object of the present invention to provide a nuclear reactor capable of producing an ultrahigh thermal neutron flux.
It is a further object of the present invention to provide a reactor capable of producing an ultrahigh thermal neutron flux intensity in an environment accessable to a large number of instruments.
It is another object of the present invention to provide a reactor capable of producing an ultrahigh neutron flux which is also capable having neutron beam lines radially orientated toward the reactor.
It is still another object of the present invention to provide an ultrahigh neutron flux reactor wherein the oxide formation on the fuel plates is held below the levels experienced in present reactors.
It is still a further object of the present invention to provide a nuclear reactor having high fission rate densities and high power densities while maintaining the total reactor power as low as possible.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combination particularly pointed out in the appended claims.